1. Field of the Invention
The present invention relates to motor vehicles and in particular to a fuel tank of a motor vehicle.
2. Description of Related Art
Motor vehicle fuel tank venting systems control the flow of fuel vapor from a vehicle fuel tank to an evaporative emission system, such a carbon canister vapor recovery device. Typically, fuel tank venting systems use valves such as pressure operated control valves, volume operated control or shutoff valves, or rollover valves, to control the passage of vapor to an evaporative emission system. While allowing the passage of vapor, the fuel tank venting systems must also prevent the flow of liquid fuel so that the liquid fuel does not reach and damage the evaporative emission system. Because the fuel tank may be inclined at different angles and orientations as a vehicle moves over varying terrain, the fuel tank venting system must prevent the flow of liquid fuel in a variety of different tank positions, and further, must accommodate a situation in which a valve might leak.
One conventional approach to preventing the flow of liquid fuel employs a half saddle or full saddle fuel tank with vent valves positioned at a high elevation point in the central region of the fuel tank, so that the tank may be tilted in any direction without submerging the valves. In this manner, the high, centrally positioned vent valves allow venting in any tilted position that the tank may assume. As an example, FIG. 1.1 illustrates a prior art half saddle fuel tank 100 having a high, centrally located vent shut float valve 102 and a high, centrally located roll over valve 104. FIG. 1.2 shows a side view of the fuel tank 100 filled to a full fuel volume and in a tilted position. As shown, the centrally located valves 102, 104 remain above the full fuel level 110 and within the vapor space 112, so as to prevent passage of liquid fuel through the valves and to the evaporative emissions canister 114.
Another conventional approach uses a tube layout that provides a sufficient head height above the liquid level in the event that fuel leaks from a valve. The tube layout allows submerging of the valve in the event of a worst case condition. Any liquid fuel that leaks past the submerged valve is unable to pass beyond the highest point in the tube, due to the head height. The liquid fuel that leaks through the valve therefore returns to the fuel tank when the tank returns to a level condition. As an example, FIG. 2.1 illustrates a prior art fuel tank 200 having a vent shut float valve 202 connected by outlet tube 203 to an evaporative emissions canister 214. The tube 203 includes a high head height portion 215 that prevents passage of liquid fuel to the evaporative emissions canister 214. FIG. 2.2 shows a side view of the fuel tank 200 filled to a full fuel volume and in a tilted position. As shown, the high head height portion 215 provides head height 205 and remains above the full fuel level 210, so as to prevent the passage of liquid fuel.
Another conventional approach uses head height and a remote valve at the top of the tube routing to control tank venting. In that configuration, the fuel level cannot reach the highest part of the tube and therefore does not enter the remote valve. As an example, FIG. 3.1 illustrates a prior art fuel tank 300 having roll over valves 304-1, 304-2, a vent shut float valve joint 301, and a remote valve and pressure control valve 302 connected to the joint 301 and positioned at a high head height 305 relative to the fuel tank 300. The valve and pressure control valve 302 is further connected to an evaporative emissions canister 314. FIG. 3.2 shows a side view of the fuel tank 300 filled to a full fuel volume and in a tilted position. As shown, the high head height 305 of the valve and pressure control valve 302 prevents passage of liquid fuel to the evaporative emissions canister 314, as the valve and pressure control valve 302 remains above the full fuel level 310.
Although the above conventional approaches may control vapor venting and limit the flow of liquid fuel, the tube and valve configurations generally are not suitable for large plan view (viewed from the top), low height (i.e., low profile) fuel tanks. A properly designed fuel system uses at a minimum one venting valve (ideal) and at most several venting valves (less ideal) that allow the fuel tank to vent when tilted at any severe angle. If the profile of a fuel tank is low, venting becomes difficult and in some cases impossible, as the valves are submerged (surrounded by fuel) and fuel leaks from the fuel tank, through the valves and tubes, and into the evaporative emission canister. The conventional techniques described above use tube routing that provides a sufficient head height to prevent fuel leaks. However, such high tube routing cannot be confined within the profile of low height fuel tanks. Manufacturers are therefore increasingly relying on zero leak valves for low height fuel tanks. Any failure in these zero leak valves can, however, cause leakage to and damage of the evaporative emission canister.
Accordingly, there remains a need for a fuel tank venting system that accommodates low profile applications while still controlling vapor control and preventing the flow of liquid to the evaporative emission canister in the event of a leaking valve.